For any of a variety of reasons, internal combustion engine systems are experiencing an increase in the use of turbochargers. As is well-known, a turbocharger includes a turbine wheel that is driven by the exhaust gases from the engine and which in turn drives a rotary compressor. The rotary compressor compresses combustion air prior to its admission to the combustion chambers of the internal combustion engine. Systems of this sort recover part of the waste energy that results when incompletely spent exhaust gases are permitted to expand without performing work and also provide for higher compression ratios than are attained by the geometry of the internal combustion engine itself.
It has long been observed that when the incoming combustion air is compressed by the turbocharger, it is simultaneously heated which in turn means that its density is decreased. Consequently, at any given pressure, a unit volume of hot air from a turbocharger contains a lesser quantity of oxygen available for combustion than would an identical volume of cold air at the same pressure. This factor in turn places a limitation on the amount of fuel that may be burned in any given operating cycle of an internal combustion engine, which in turn limits the output thereof. Consequently, particularly in vehicular applications, a so-called charge air cooler has been introduced between compressor stages or between the compressor side of the turbocharger and the intake manifold (or equivalent) for the internal combustion engine. The hot, combustion air from the turbocharger is passed through the charge air cooler to the engine. At the same time, ambient air is being passed through the charge air cooler in a flow path isolated from the combustion air, but in heat exchange relation therewith. Consequently, cooling of the combustion air is obtained to increase the density of the combustion air to ultimately provide a greater quantity of oxygen per charge of air to the engine to support combustion.
It can readily be appreciated that even though the elevated pressure of the combustion air results in a relatively small pressure differential with ambient, charge air coolers operate in relatively stressful environments. Typically, because they are employed in vehicular installations, they are subject to a great deal of vibration and shock as the vehicle travels over the underlying terrain.
Furthermore, they are subject to thermal cycling, that is, alternating heating and cooling, not only as the vehicle engine is turned on or off, but during operation of the same at varying speeds. Changes of combustion air velocity with varying engine speed within the tanks of a typical charge air cooler may result in temperature gradients as high as 25.degree. F. from one tube to the next which, over a period of time, can result in substantial stress at tube to header joints.
Finally, even though as mentioned previously, typical charge air coolers do not operate at pressures significantly above ambient, because charge air coolers are required to pass a large volume of combustion air to the engine with minimal resistance, large flow paths are employed, which in turn are defined by surfaces of a relatively large area. And where even extremely low pressure differentials are applied across large surface areas, those skilled in the art will appreciate that substantial forces exist, thus putting further stress on charge air cooler components.
The present invention is directed to overcoming one or more of the above problems.